Drill bit for percussive drilling

ABSTRACT

A drill bit for use in percussive drilling includes a body having a front face, at least one face button on the front face, and a plurality of gauge buttons. Each of the buttons has a working face. At least a portion of at least one gauge button working face has a curvature which deviates further from being flat by comparison to a curvature of any curved portion of at least one face button working face, so that the portion of at least one gauge button working face projects further than the portion of at least one face button working face.

For the purpose of explanation reference will be made to use of the drill bit in top hammer percussive drilling of rock, but it can also be used in other kinds of percussive drilling, such as DTH.

Buttons or inserts for bits of this type generally have a cylindrical body with opposing ends, one of which comprises a working face for the button that is shaped so as to protrude from the body of the button. More particularly, this working face is generally hemispherical (domed) or parabolic (ballistic) in shape.

Typically, gauge buttons have a diameter which is larger than or equal to face buttons. Examples of this can be found in U.S. Pat. No. 3,519,092, U.S. Pat. No. 3,997,011 and U.S. Pat. No. 4,572,307 amongst others, as well as being illustrated in FIG. 2 herein.

A problem with bits of the above described type is that an extent of reflected energy (ie. reflected from the rock face) is so great that this can damage the bit and other associated equipment.

In U.S. Pat. No. 5,947,215 there is disclosed a drill bit having a single, centrally positioned front button which is of larger diameter than the gauge buttons, and wherein forwardmost portions of the gauge buttons and front button lie in a common plane, or the front button is more forwardly projecting. The object of this is to provide good bit guidance.

It is against this background and the problems and difficulties associated therewith that the present invention has been developed.

The objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

SUMMARY OF THE INVENTION

In one aspect, the invention may be said to reside in a drill bit for use in percussive drilling, the drill bit comprising a body having a front face, at least one button on the front face (hereinafter ‘face button’), and a plurality of gauge buttons, each of the buttons having a working face, at least a portion of at least one gauge button working face having a curvature which deviates further from being flat (ie. is more pronounced, pointed or sharper) than a curvature of any curved portion of at least one face button working face so that said portion of at least one gauge button working face projects further than said portion of at least one face button working face.

In the context of the present application the term ‘working face’ should be taken to mean the part of each button which will interact with the rock during drilling.

In one form, said portion of at least one gauge button working face projects further than said portion of at least one face button working face.

In one form, at least a portion of the working face of each of the face and gauge buttons is curved. In case said working face (10 a and 20 a) comprises multiple portions, each portion may blend into adjacent portions.

In one form, the entirety of the working face of each of the face and gauge buttons is curved.

In one form, the curvature of the working face of at least one gauge button is more pronounced than the curvature of the working face of at least one face button.

In one form, the or each gauge button working face projects further than the or each face button working face.

In one form, a radius of curvature of the working face of at least one face button is greater than a radius of curvature of the working face of at least one gauge button.

In one form, each of the face and gauge buttons includes a substantially cylindrical body.

In one form, the working face of at least one gauge button is substantially hemispherical (or domed).

In one form, the working face of at least one gauge button is substantially parabolic (or ballistic) in shape.

In one form, the working face of at least one face button is shaped like a segment of a hemisphere (or dome).

In one form, the working face of at least one face button is shaped like a segment of a parabola (or ballistic shape).

In one form, the cylindrical body of at least one face button has a radius which is different to a radius of curvature of the curved portion of the working face thereof.

In one form, the radius of the cylindrical body of at least one face button is less than the radius of curvature of the curved portion of the working face thereof.

In one form, the cylindrical body of at least one gauge button has a radius which is substantially equal or at least similar to a radius of curvature of the curved portion of the working face thereof.

In one form, the drill bit comprises a plurality of face buttons.

In one form, the working face of at least one face button is or is approaching substantially flat.

In a further aspect, the invention may be said to reside in a drill bit for use in percussive drilling, the drill bit comprising a body having a front face, at least one button on the front face (hereinafter ‘face button’), and a plurality of gauge buttons, each of the buttons having a working face, the drill bit being characterised in that at least a portion of at least one gauge button working face has a curvature with a peak that is more projecting by comparison to a peak of any curved portion of at least one face button working face.

In one form, the or each face button is offset with respect to the central axis of the bit.

A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications and equivalents. For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention.

The present invention may be practiced according to the claims without some or all of lip these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of this disclosure it will now be described with respect to an exemplary embodiment which shall be described herein with the assistance of drawings wherein:

FIG. 1 is a longitudinal section through the body of a drill bit; and

FIG. 2 is cross-sectional view through the body of a prior art drill bit.

In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIG. 1, where there is illustrated a drill bit (1) for use in percussive drilling. The drill bit (1) comprises a bit body (2) of an appropriate tool steel grade having a front face (4) which extends generally transversely relative to a longitudinal axis of the bit body (2), and a rear threaded portion (6) so the drill bit (1) can be threadably attached to a drill rod (not illustrated) having corresponding threads.

Located in the front face (4) is a plurality of face buttons (10) which project and protrude axially therefrom.

Located around the periphery of the face (4) is a plurality of gauge buttons (20) inclined at an angle with respect to the longitudinal axis of the bit (1). The gauge buttons (20) project and protrude to such an extent that the diameter of the drill hole is defined by these.

The buttons (10 and 20) are either press-fit or shrink-fit into the bit body (2), and so are commonly and even interchangeably referred to as inserts. The buttons (10 and 20) are formed of a material which is harder than the material of the bit body (2).

Each button (10 and 20) has a cylindrical body with a working face (10 a) in one case, and (20 a) in the other, the working face being the part of each button (10 and 20) which will interact with the rock during drilling. In this embodiment, each of these working faces (10 a and 20 a) is convexly curved. The projecting distance F of the face button working face (10 a) and the projecting distance G of the gauge button working face (20 a) are measured from the associated body portion as shown in FIG. 1, wherein G is greater than F.

Each gauge button (20) working face (20 a) has a curvature which is more pronounced than a curvature of at least one face button (10) working face (10 a). That is to say, a radius of curvature (RF) of the working face (10 a) of the face buttons (10), is significantly greater than a radius of curvature (RG) of the working face (20 a) of the gauge buttons (20).

What is more, in the case of the face buttons (10), the radius of curvature of the working face (RF) is significantly greater than a radius (R′) of the cylindrical body thereof. In contrast, for each of the gauge buttons (20), the radius of curvature of the working face (RG) is generally the same as a radius (R″) of the cylindrical body thereof.

In the case of the face buttons (10) then, the radius of curvature (RF) of the working face (10 a) may be so great that the working face approaches, or is, a substantially flat surface, the face button (10) working face (10 a) thereby having no or minimal projection, and certainly less projection that the gauge button (20) working face (20 a).

Tests which have been carried out indicate that the force required to penetrate the rock is less with a more pointed button such as the gauge buttons (20), than with a blunter one such as the face buttons (10).

Given then, that for any rock and any drill hole therein the penetration resistance will be higher in a corner between an end and side of the hole than at the end of hole where the rock face is flat, it advantageous if, as per the present invention, the working face (20 a) of the gauge buttons (20) is more pointed than the working face (10 a) of the face buttons (10), as less force will be required for penetration, resulting in less wastage of percussive energy and less reflected energy in turn. Less reflected energy means less damage to drill and other associated equipment.

A further advantage of the above described drill bit (1) is higher drill speed and improved drilling efficiency when compared with bits of the prior art, such as that illustrated at FIG. 2.

All gauge buttons in the drill bit may be substantially identical in shape. All face buttons in said or a drill bit may be substantially identical in shape.

Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprising” and “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications in its scope. 

1. A drill bit for use in percussive drilling, the drill bit comprising; a body having a front face; at least one face button on the front face; and a plurality of gauge buttons, each of the face and plurality of gauge buttons having a working face, wherein at least a portion of at least one gauge button working face has a curvature which deviates further from being flat by comparison to a curvature of any curved portion of the at least one face button working face, so that said portion of at the least one gauge button working face projects further than said portion of at least one face button working face.
 2. The drill bit of claim 1, wherein at least a portion of the working face of each of the face and plurality of gauge buttons is curved.
 3. The drill bit of claim 2, wherein the entirety of the working face of each of the face and plurality of gauge buttons is curved.
 4. The drill bit of claim 3, wherein the curvature of the working face of at least one gauge button deviates further from being flat than the curvature of the working face of at least one face button.
 5. The drill bit of claim 3, wherein each gauge button working face projects further from its associated body portion than the or each face button working face.
 6. The drill bit of claim 3, wherein the working face of at least one gauge button is substantially hemispherical.
 7. The drill bit of claim 3, wherein the working face of at least one face button is substantially shaped like a segment of a hemisphere.
 8. The drill bit of claim 1, wherein each of the face and plurality of gauge buttons includes a substantially cylindrical body.
 9. The drill bit of claim 1, further comprising a plurality of face buttons.
 10. The drill bit of claim 1, further comprising a central axis, and each face button is offset with respect to the central axis.
 11. The drill bit of claim 1, wherein the working face of at least one face button is substantially flat. 